Direct mountain front recharge (MFR), groundwater recharge to the water table from a mountain block and adjacent mountain front, in an arid environment (<250 mm yr-1 precipitation) was calculated using water level and precipitation data for two catchments in the Silver Island Mountains, Utah, USA. One catchment was bedrock dominated (mountain block) and one catchment was alluvial fan dominated (mountain front). The catchments range in size form 17.5 to 25.6 km2.
Direct MFR occurs throughout much of the year in response to even small rainfall events and snowmelt was not necessary for direct MFR. Normalized to one year, direct MFR was calculated as 0.02-0.03% precipitation for both catchments, with seasonal rates of 0.00% in summer months and up to 0.03% in winter/spring and fall months. Seasonal differences in direct MFR were similar in both bedrock and alluvial fan dominated catchments.
There was a fast response between precipitation events and water level responses at the outlet of the catchments. The time lag between precipitation events and groundwater level responses was greater in the mountain block catchment than the mountain front catchment, 2 and 1 month, respectively. Direct MFR was 10% or less than literature reported typical calculated combined MFR (near surface and deep underflow) for similar terrains and climates.
The direct MFR was only 3.5% of the combined MFR for the Silver Island Mountains using the Maxey-Eakin method. However, based on total recharge to the adjacent playa, the direct MFR is at least 50% of the combined MFR.